1. Technical Field
The present invention relates to a method for the generation of a voltage for the purpose of detecting an ionization current in the spark gap of an internal combustion engine. The detection is supposed to take place after the ignition of the spark and after the decay of the spark.
2. Description of the Prior Art
It is known that the combustion of an air/fuel mixture in an internal combustion engine results in the production of ions. These ions can be detected by applying a voltage across the spark gap with the result that an ionization current is generated. This ionization current can be measured and used for the detection of misfire, knock, missing combustion, combustion quality and so on, of the engine.
The measurement of the ionization current attained in the spark gap can take place either on the high tension side of the spark device or on the low tension side.
On the high tension side, a measurement problem is the difficulty of handling the generated voltage (up to about 50 kV) by means of commercially available electronic components. Due to these problems the ionization current measurement takes place on the low tension side of the spark device today. According to this method there are problems as well, that is to say component tolerance problems and leakage currents coming into existence in components and coils and causing interpretation uncertainty of the measurements carried out. Furthermore, the spark itself disturbs the measurements of the ionization current when the spark current and ionization current are time-connected to each other, and the differences of the amplitudes are about 1000 times. Another problem is that the ionization current amplitude is influenced by gasoline additives.
The technique of today for the purpose of measuring an ionization current is based on the discharge of a DC voltage of about 100 V being stored in a capacitor arranged for that purpose in the secondary circuit of the ignition device, which DC voltage is discharged via the spark device in connection with the generation of the spark. This voltage gives rise to a varying ionization current, where the ion current level depends on the number of free ions. A change of the number of the ions changes the conductivity between the electrodes.
Ignition knock, misfire, combustion quality and so on can be read from the ionization current by means of signal processing, such as frequency separation and other mathematical signal processing.